Date - 09/04/2020

ALLAHABAD PUBLIC SCHOOL

Class - IX

Subject - Science ( chemistry )

Chapter - Matter in our surroundings

By - Amala Shankar Sir

Comparison of characteristic properties of Solids, liquids

and gases :

The common unit of Temperature and SI unit of

Temperature :

The common unit of measuring temperatures like

melting points, boiling points, etc is 'degrees Celcius

(°C)' read as degrees C.

The melting point of ice on Celcius scale of

temperature is 0°C (zero degree Celsius), and

the boiling point of water on Celcius scale is

100°C.

There is another scale of temperature called

Kelvin scale of temperature which is used by the

scientists mainly for research work.

The SI unit of measuring temperature is Kelvin

(K).

The melting point of ice on Kelvin scale is 273K.

And the boiling point of water on Kelvin scale is

373K.

Temperature on Kelvin scale = Temperature on

Celcius scale + 273

0°C = 273K

Change of state of matter :

We can change the physical state of matter in two ways :

1. By changing the temperature, and

2. By changing the pressure.

Effect of change of temperature :

1. Solid to liquid change : Melting

Ice is a solid. In solids, the particles are tightly packed

together. When we heat a solid, its particles become

more energetic and kinetic energy of the particles

increases. Due to the increase in kinetic energy, the

particles start vibrating more strongly with greater speed.

The energy supplied by heat overcomes the

intermolecular forces of attraction between the particles.

As a result, the particles leave their mean position and

break away from each other. After this solid melts and a

liquid is formed.

Melting point : The melting point at which a solid melts

to become a liquid at the atmospheric pressure is called

its melting point. The process of melting is also called

"fusion". The melting point of ice is 0°C. It may also be

written as 273.16K or 273K.

Melting point of iron is 1535°C.

Melting point of wax is 63°C.

Melting point of ice is 0°C.

2. Liquid to gas change : Boiling (or vaporization)

The process in which a liquid substance changes into a

gas rapidly on heating, is called boiling. The temperature

at which a liquid boils and changes rapidly into a gas at

atmospheric pressure, is called boiling point of the liquid.

Boiling point of water is 100°C.

Boiling point of alcohol is 78°C.

Boiling point of mercury is 357°C.

The boiling point of liquid is a measure of the force of

attraction between its particles.

3. Gas to liquid change : Condensation

The process of changing a gas (or vapour) to a liquid by

cooling,is called condensation. Condensation is the

reverse process of boiling ( or vaporisation ).

4. Liquid to solid change : Freezing

The process of changing a liquid into a solid by cooling,

is called freezing. Freezing means solidification.

Freezing is the reverse of melting.

Freezing point of water is 0°C.